Method for producing extra force and reduced hydraulic supply for shearing pipe

ABSTRACT

The method of providing blowout preventer ram actuator which will move a blowout preventer shear ram into the bore of the blowout preventer and retract the blowout preventer shear ram from the bore of the blowout preventer, comprising providing a first and second piston, pressuring the second cylinder extension area to move the blowout preventer shear ram into contact with the pipe to be sheared while venting the second cylinder, sensing that the blowout preventer shear ram has contacted the pipe to be sheared, pressuring the first and the second cylinder to shear the pipe and pressuring the first cylinder to retract the shear ram.

TECHNICAL FIELD

This invention relates to the method of providing a high force by hydraulic fluid to blowout preventer shear rams while reducing the volume of hydraulic fluid and size of hydraulic accumulators required.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable

REFERENCE TO A “MICROFICHE APPENDIX”

Not applicable

BACKGROUND OF THE INVENTION

Deepwater offshore drilling requires that a vessel at the surface be connected through a drilling riser and a large blowout preventer stack to the seafloor wellhead. The seafloor wellhead is the structural anchor piece into the seabed and the basic support for the casing strings which are placed in the well bore as long tubular pressure vessels. During the process of drilling the well, the blowout preventer stack on the top of the subsea wellhead provides the second level of pressure control for the well. The first level being provided by the weighted drilling mud within the bore.

During the drilling process, weighted drilling mud circulates down a string of drill pipe to the drilling bit at the bottom of the hole and back up the annular area between the outside diameter of the drill pipe and the inside diameter of the drilled hole or the casing, depending on the depth.

Coming back up above the blowout preventer stack, the drilling mud will continue to travel back outside the drill pipe and inside the drilling riser, which is much large than the casing. The drilling riser has to be large enough to pass the casing strings run into the well, as well as the casing hangers which will suspend the casing strings. The bore in a contemporary riser will be at least twenty inches in diameter. It additionally has to be pressure competent to handle the pressure of the weighed mud, but does not have the same pressure requirement as the blowout preventer stack itself.

As wells are drilled into progressively deeper and deeper formations, the subsurface pressure and therefore the pressure which the blowout preventer stack must be able to withstand becomes greater and greater. This is the same for drilling on the surface of the land and subsea drilling on the surface of the seafloor. Early subsea blowout preventer stacks were of a 5,000 p.s.i. working pressure, and over time these evolved to 10,000 and 15,000 p.s.i. working pressure. As the working pressure of components becomes higher, the pressure holding components naturally become both heavier and taller. Additionally, in the higher pressure situations, redundant components have been added, again adding to the height. The 15,000 blowout preventer stacks have become in the range of 800,000 lbs. and 80 feet tall. This provides enormous complications on the ability to handle the equipment as well as the loadings on the seafloor wellhead. In addition to the direct weight load on the subsea wellheads, side angle loadings from the drilling riser when the surface vessel drifts off the well centerline are an enormous addition to the stresses on both the subsea wellhead and the seafloor formations.

Shear rams within these blowout preventers are utilized to shear pipe only in emergency cases when there is not other solution to securing a subsea well installation. Securing the well involves both the steps of shearing the pipe in half and then providing a seal across the well bore. Ideally a single blowout preventer ram will be equipped with shear rams which upon actuation will shear and seal in a single movement and then provide a seal which is compression set. Being compression set is beneficial as the extreme destructive nature of cutting high strength pipe in half tends to damage any kind of seal, and a compression set seal is the most “self-healing” type of seal. The high pressures generated by being compression set will tend to seal over many defects in the seal.

It can be sometimes presumed that the sheared section of pipe above the shear ram will be yanked out of the seal area upon shearing if the pipe is in its normal tension is a subsea drilling system. This is not always true, and was not true in the 2010 Gulf of Mexico Macondo blowout case.

One solution provided for this is to have a seal which seal in the shear plane as a face seal. This seal is dependent upon not scratching the seal or the mating seal surfaces, and that no shrapnel from the shearing operation gets in the way.

Another solution which has been provided is to literally bend the pipe out of the way. This has worked on some section of pipe, but with extreme high strength pipe and connections used today, there is great difficulty in bending the pipe and coupling sections.

The shearing of the pipe and casing available today requires very high forces and when you add lifting or bending of the pipe out of the way of the seals the forces are even higher. This is in direct conflict with the need for reduced accumulator volumes to operate the shear rams. The ideal solution here is to provide a maximum shearing force with a minimum of hydraulic accumulator volume required.

BRIEF SUMMARY OF THE INVENTION

The object of this invention is to provide blowout preventer shear rams with a high shear force to shear pipe in the bore of the blowout preventer.

A second object of this invention is to minimize the hydraulic supply required to perform the shearing operations.

A third object of this invention is to sense the need for high force requirements rather than low volume requirements by sensing the operating pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of a contemporary deep-water riser system.

FIG. 2 is a perspective view of a blowout preventer stack utilizing the features of this invention.

FIG. 3 is a perspective view of a subsea wellhead housing which the blowout preventer stack of this invention would land on.

FIG. 4 is a perspective view of the lower portion of the blowout preventer stack of FIG. 2 , generally called the lower BOP stack.

FIG. 5 is a perspective view of the upper portion of the blowout preventer stack of FIG. 2 , generally called the lower marine riser package or LMRP.

FIG. 6 is a perspective view of a section of the drilling riser which will be used to lower the blowout preventer stack.

FIG. 7 is a view of the blowout preventer stack of FIG. 2 , taken along lines “7-7.

FIG. 8 is a view of the blowout preventer stack of FIG. 2 , taken along lines "8-8.

FIG. 9 is a top view of FIG. 8 .

FIG. 10 is a perspective view of a pair of shear rams spaced apart.

FIG. 11 is a perspective view of the pair of shear rams of FIG. 10 moved closer together.

FIG. 12 is a perspective view of a lower shear ram with the lifter in the initial position.

FIG. 13 is a perspective view of a lower shear ram of FIG. 12 with the lifter rotated to a raised position as it would be during operation when the sheared pipe is raised.

FIG. 14 shows a cross section view of a shear ram blowout preventer with the rams in the fully opened condition.

FIG. 15 shows a figure similar to FIG. 14 with the shear rams moved to a position of having just sheared the pipe.

FIG. 16 shows a figure similar to FIG. 15 with the shear rams moved to a position closer to one another and having raised the sheared section of pipe above the level of the seal.

FIG. 17 shows a figure similar to FIG. 16 with the shear rams moved fully into contact and into face-to-face sealing engagement.

FIG. 18 shows a shear ram actuator with two pistons which will be moved forward to the point of shearing contact by pressuring only one of the pistons.

FIG. 19 shows a shear ram actuator with two pistons and both of them being pressured to do the actual pipe shearing.

FIG. 20 shows a shear ram actuator with two pistons with the shear ram and pistons being retracted by pressuring only one of the pistons.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1 , a view of a system 20 which might use the present invention is shown. It shows a floating vessel 22 on a body of water 24 and having a derrick 26. Drill pipe 28, drilling mud system 30, control reel 32, and control cable 34 are shown. A riser system 40 including a flex joint 42 is shown. During drilling the drilling mud circulated from the drilling mud system 30, up the standpipe 44, down the drill pipe 28, through the drill bit 46, back up through the casing strings 48 and 50, through the blowout preventer stack 60, up thru the riser system 40, and out the bell nipple at 62 back into the mud system 30.

Blowout preventer stack 60 is landed on a subsea wellhead system 64 landed on the seafloor 66. The blowout preventer stack 60 includes pressurized accumulators 68, kill valves 70, choke valves 72, choke and kill lines 74, choke and kill connectors 76, choke and kill flex means 78, and control pods 80.

Referring now to FIG. 2 , the seafloor drilling system 100 comprises a lower blowout preventer stack 102, a lower marine riser package 104, a drilling riser joint 106, and control cables 108.

Referring now to FIG. 3 , a subsea wellhead is shown which the seafloor drilling system lands on. It is the unseen upper portion of the subsea wellhead system 64 shown in FIG. 1 .

Referring now to FIG. 4 , the lower blowout preventer stack 102 comprises a lower structural section 120, vertical support bottle 122, and upper structural section 124, accumulators 126, choke and kill valves 128, blowout preventers 130 and an upper mandrel 132 which will be the connection point for the lower marine riser package.

Referring now to FIG. 5 the lower marine riser package 104 is shown comprising a lower marine riser package structure 140, an interface 142 for a remotely controlled vehicle (ROV), annular blowout preventers 146, choke and kill flex loops 148, a flexible passageway 150, a riser connector 152, and an upper half of a riser connector 154.

Referring now to FIG. 6 , a drilling riser joint 106 is shown having a lower half of a riser connector 160, a upper half of a riser connector 154, and buoyancy sections 162.

Referring now to FIG. 7 , is a view of seafloor drilling system 100 taken along lines “7-7” of FIG. 1 showing wellhead connector 170, lower marine riser connector 172, a man 174 for size perspective, and choke and kill valves 176.

Referring now to FIG. 8 , is a view of seafloor drilling system 100 taken along lines “8-8” of FIG. 1 .

Referring now to FIG. 9 , is a top view of seafloor drilling system 100.

Referring now to FIG. 10 which is a perspective view of a pair of shear ram 200 of this present invention including lower shear ram 202 and upper shear ram 204. Lower shear ram 202 has lower shear blade 206, lifter 208, body 210 and body seal 212. Upper shear ram 204 has upper shear blade 214, lifter 216, body 218, body seal 220, and front seal portion 222.

Referring now to FIG. 11 , lower shear ram 202 and upper shear ram 204 are moved closer to one another such that the upper shear blade 214 is passing above lower shear blade 206 as any pipe in the blowout preventer bore is being sheared.

Referring now to FIG. 12 , lower shear ram 202 is shown in greater detail. Front portion 230 of body seal 212 is shown, and this is where the front face of upper shear blade 214 will contact to seal across the bore of the blowout preventer. It can be noted that the lifter 208 remains in the same location as seen in FIGS. 10 and 11 .

Referring now to FIG. 13 , lifter 208 is shown in the rotated position after the pipe is sheared and has been lifted.

Referring now to FIG. 14 which shows a shear ram blowout preventer in the fully opened condition, blowout preventer body 300 is shown having a central bore 302, ram cavities 304 and 306, and an injection port 308. Upper shear ram 204 has actuating rod 312, body seal 220, upper shear blade 214, pipe lifter 216, front curved surface 320, pivot pin 322, and a rear curved or cylindrical surface 324. Lower shear ram 202 has actuating rod 332, lower shear blade 206, front seal 336, body seal 212, and pipe lifter 208 with pivot pin 342 and rear curved or cylindrical surface 344.

Referring now to FIG. 15 which shows upper shear ram 204 and lower shear ram 202 moved forward to the point that pipe 350 in the bore as just being sheared into upper pipe section 352 and lower sheared section 354 and the pipe lifters 208 and 216 are contacting upper pipe section 352.

Referring now to FIG. 16 which shows as the upper shear ram 204 and lower shear ram 202 have continued to move forward to lift upper pipe 352 to an elevation above the front seal 336 by pivoting the pipe lifters 208 and 216 about pivot pins 322 and 342 and sliding about rear curved surfaces 324 and 344. The purpose of the rear curved surfaces 324 and 344 is to withstand any high loadings in this process as a bearing load rather than a shear load on the pivot pins 322 and 342.

Referring now to FIG. 17 which shows upper shear ram 204 has engaged and sealed with lower shear ram 202 with the front seal 336 sealing against the front of upper shear blade 214 at 356. In this way the lower sheared section 354 remains below the shear and seal plane and the upper seared section 352 has been automatically lifted sufficiently to allow a conventional face-to-face seal between the upper and lower shear rams 310 and 330. This avoids the conventional problems of having to literally bend one of the sheared pipe ends out of the way or settling for a sliding seal at the shear plane rather than a superior face-to-face compression set seal. Additionally groove 356 is provided as a passageway for a plastic packing sealant material which can be injected into the blowout preventer body 300 at the injection port 308 seen in FIG. 14 as a secondary seal means if there turns out to be a defect in the primary seal 336. The preferred embodiment described utilizes pivoting plates to lift the sheared section of pipe to allow the sealing, however, other motions such as an angled sliding action are also possible.

Referring now to FIG. 18 blowout preventer body 400 has shear ram 402 presently in the position of being retracted from the bore of the blowout preventer and being connected to piston rod 404 and in turn to piston 406. Piston rod 408 is also shown connected to 410. To move shear ram 402 into position to shear hydraulic fluid is introduced into the rear of piston 410 through fitting 432 as indicated by the arrow 430. As hydraulic fluid introduced into fitting 432 will move piston 410 forward or to the right, it will also tend to move piston rod 408, piston 406, and piston rod 404 forward also. By venting the ports 434, 436, and 438 to allow flow in either direction a shown by arrows 440, flow will be drawn from the reservoir into fitting 436 and be expelled to the reservoir through fittings 434 and 438.

Referring now to FIG. 19 , when the pressure in fitting 432 builds up to more than is required to simply move the components towards the pipe indicating that the pipe has been engaged, the control circuitry is changed to input pressurized hydraulic fluid into fittings 432 and 436 as indicated by arrows 450 and fittings 434 and 438 are directed to the hydraulic reservoir. This has meant that most of the travel of the shear rams has been accomplished with half the fluid volume required to actually shear the pipe, with the actual volume being required only for the last portion.

Referring now to FIG. 20 , if hydraulic fluid is introduced into fitting 438 as piston 404 is pushed to the rear it will move the shear ram 402 and piston 410 with it, again at half the volume required for shearing.

The same economies of accumulator can also be applied to any of the other rams in a blowout preventer stack.

The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.

SEQUENCE LISTING: N/A 

That which is claimed is:
 1. The method of providing blowout preventer ram actuator which will move a blowout preventer shear ram into the bore of the blowout preventer and retract the blowout preventer shear ram from the bore of the blowout preventer, comprising providing a first piston with a piston rod connected to the blowout preventer shear ram in a first cylinder, the first cylinder having a first [an first] cylinder extension area for extending the blowout preventer shear ram into the bore of the blowout preventer and a first cylinder retraction area for retracting the blowout preventer shear ram from the bore of the blowout preventer, providing a second piston in a second cylinder which is connected to the first cylinder, the second cylinder having a second cylinder extension area for extending the blowout preventer shear ram into the bore of the blowout preventer and a second cylinder retraction area, pressuring the second cylinder extension area to move the blowout preventer shear ram into contact with the pipe to be sheared while venting the second cylinder retraction area, the first cylinder extension area, and the first cylinder retraction area, sensing that the blowout preventer shear ram has contacted the pipe to be sheared, pressuring the second cylinder extension area and the first cylinder extension area and venting the first cylinder retraction area and the second cylinder retraction area to shear the pipe in the bore of the blowout preventer.
 2. The method of claim 1, providing pressuring the first cylinder retraction area while venting the first cylinder extension area, the second cylinder extension area, and the second cylinder retraction area to retract the blowout preventer shear ram from the bore of the blowout preventer.
 3. The method of claim 1, providing sensing that the blowout preventer shear ram has contacted the pipe to be sheared is by sensing the pressure in the second cylinder extension area.
 4. The method of providing blowout preventer ram actuator which will move a blowout preventer shear ram into the bore of the blowout preventer and retract the blowout preventer shear ram from the bore of the blowout preventer, comprising providing a first piston in a first cylinder, the first piston having a piston rod connected to the blowout preventer shear ram_(:) the first cylinder having a first cylinder extension area for extending the blowout preventer shear ram into the bore of the blowout preventer and a first cylinder retraction area for retracting the blowout preventer shear ram from the bore of the blowout preventer, providing a second piston in a second cylinder which is connected to the first cylinder, the second cylinder having a second cylinder extension area for extending the blowout preventer shear ram into the bore of the blowout preventer and a second cylinder retraction area, pressuring the second cylinder extension area to move the blowout preventer shear ram into contact with the pipe to be sheared while venting the second cylinder retraction area, the first cylinder extension area, and the first cylinder retraction area, sensing that the blowout preventer shear ram has contacted the pipe to be sheared, pressuring the second cylinder extension area and the first cylinder extension area and venting the first cylinder retraction area and the second cylinder retraction area to shear the pipe in the bore of the blowout preventer, and shearing the pipe in the bore of the blowout preventer.
 5. The method of claim 4, providing pressuring the first cylinder retraction area while venting the first cylinder extension area, the second cylinder extension area, and the second cylinder retraction area to retract the blowout preventer shear ram from the bore of the blowout preventer.
 6. The method of claim 4, providing sensing that the blowout preventer shear ram has contacted the pipe to be sheared is by sensing the pressure in the second cylinder extension area. 